The Unicode Standard defines a surrogate pair as a coded character representation for a single abstract character that consists of a sequence of two code units, where the first unit of the pair is a high surrogate and the second is a low surrogate. A high surrogate is a Unicode code point in the range U+D800 through U+DBFF and a low surrogate is a Unicode code point in the range U+DC00 through U+DFFF.

A control character is a character for which the Unicode value is U+007F or in the range U+0000 through U+001F or U+0080 through U+009F.

The .NET Framework defines a text element as a unit of text that is displayed as a single character, that is, a grapheme. A text element can be a base character, a surrogate pair, or a combining character sequence. The Unicode Standard defines a combining character sequence as a combination of a base character and one or more combining characters. A surrogate pair can represent a base character or a combining character.

If a combining character sequence is invalid, every combining character in that sequence is also returned.

Each index in the resulting array is the beginning of a text element, that is, the index of the base character or the high surrogate.

The length of each element is easily computed as the difference between successive indexes. The length of the array will always be less than or equal to the length of the string. For example, given the string "\u4f00\u302a\ud800\udc00\u4f01", this method returns the indexes 0, 2, and 4.

Starting in version 2.0 of the .NET Framework, the SubstringByTextElements method and LengthInTextElements property provide an easy to use implementation of the functionality offered by the ParseCombiningCharacters method.

usingnamespace System;
usingnamespace System::Text;
usingnamespace System::Globalization;
// Show how to enumerate each real character (honoring surrogates)// in a string.void EnumTextElements(String^ combiningChars)
{
// This StringBuilder holds the output results.
StringBuilder^ sb = gcnew StringBuilder();
// Use the enumerator returned from GetTextElementEnumerator// method to examine each real character.
TextElementEnumerator^ charEnum =
StringInfo::GetTextElementEnumerator(combiningChars);
while (charEnum->MoveNext())
{
sb->AppendFormat("Character at index {0} is '{1}'{2}",
charEnum->ElementIndex, charEnum->GetTextElement(),
Environment::NewLine);
}
// Show the results.
Console::WriteLine("Result of GetTextElementEnumerator:");
Console::WriteLine(sb);
}
// Show how to discover the index of each real character// (honoring surrogates) in a string.void EnumTextElementIndexes(String^ combiningChars)
{
// This StringBuilder holds the output results.
StringBuilder^ sb = gcnew StringBuilder();
// Use the ParseCombiningCharacters method to// get the index of each real character in the string.array <int>^ textElemIndex =
StringInfo::ParseCombiningCharacters(combiningChars);
// Iterate through each real character showing the character// and the index where it was found.for (int i = 0; i < textElemIndex->Length; i++)
{
sb->AppendFormat("Character {0} starts at index {1}{2}",
i, textElemIndex[i], Environment::NewLine);
}
// Show the results.
Console::WriteLine("Result of ParseCombiningCharacters:");
Console::WriteLine(sb);
}
int main()
{
// The string below contains combining characters.
String^ combiningChars = L"a\u0304\u0308bc\u0327";
// Show each 'character' in the string.
EnumTextElements(combiningChars);
// Show the index in the string where each 'character' starts.
EnumTextElementIndexes(combiningChars);
};
// This code produces the following output.//// Result of GetTextElementEnumerator:// Character at index 0 is 'a-"'// Character at index 3 is 'b'// Character at index 4 is 'c,'//// Result of ParseCombiningCharacters:// Character 0 starts at index 0// Character 1 starts at index 3// Character 2 starts at index 4